Abstract: To judge the danger degree of current situation accurately and intuitively, fully utilizing the known information of inter-vehicle movement and based on safe time headway model, a new modeling method of time-to-crash (TTC) is proposed. An active collision avoidance system conforming to the collision avoidance characteristics of driver is developed based on the risk judging indicator TTC. A hierarchic braking strategy for collision avoidance is designed, whose key parameters are determined based on driver’s characteristics and real vehicle test results. In addition, a warning threshold Tw is introduced and an active collision avoidance warning strategy in audible and visual forms is designed to help driver fulfill effective collision avoidance. The results of real vehicle test show that the hierarchic braking and warning strategy of the system conform to driver’s characteristics, embody the priority and coordination of driver’s control, and can effectively avoid crash, meeting the requirements of active collision avoidance of vehicles

Key words: active collision avoidance, safe time headway model, time to collision, hierarchic braking, warning threshold